1. Field of the Invention
The present invention relates to a high performance photoluminescent material and a production method therefor. More particularly, the invention relates to a novel high performance photoluminescent material and a production method therefor, the material featuring quite a high photoluminescence performance with long lasting visible effect and finding beneficial applications in finishing materials for use with construction materials or civil engineering work materials, a variety of sign materials or marking materials, and installations using such materials.
2. Background Art
Conventionally, an artificial stone material has been known which is prepared by crushing natural stone, mixing the crushed stone with resin or the like, and solidifying the mixture. Various approaches have been taken to provide an artificial stone material featuring a natural stone like design, such as of marble, granite or the like, and also having high hardness and strength.
As an approach to improve the function or performance of such an artificial stone material, the use of a photoluminescent material for imparting a light emitting function is proposed.
For example, a luminescent tile has been proposed, which contains an inorganic filler material, a synthetic resin and a photoluminescent pigment, the inorganic filler material used in concentrations of about 50 wt % or more based on the total weight of the tile (JP-A-60-137862). The luminescent tile is produced as follows. A composition is prepared by blending together 75 wt % of inorganic filler of quartz sand having a mean particle size of at least 0.2 mm, 15 wt % of resin syrup containing an MMA polymer and an MMA monomer in a weight ratio of 25/75, and 9 wt % of photoluminescent pigment. The resultant composition is mold cured into a sheet having a thickness of 3 to 5 mm.
In the case of the luminescent material containing the photoluminescent pigment as described, however, energy saturation obtained from a D65 normal light source of 200 Lx can provide luminescence at a brightness of at least 3 mcd/m2 for no more than a few hours. The above brightness is a low limit to permit the human naked eyes to recognize a contour of an object. The material disclosed in the above publication (JP-A-60-137862) provides luminescence lasting for no more than 1 hour.
Furthermore, the above material also has a problem of an insufficient initial luminescence brightness, or cannot provide such an luminescence as to maintain a sufficient level of brightness for clear visible recognition of objects for a period of about 15 minutes. Such an luminescence period is considered to be necessary for evacuation guide in the event of power failure.
Although the luminescent material incorporates therein the photoluminescent pigment, a surface or at most a 1-mm-deep portion of the material is available for light emission while the photoluminescent pigment present at the deeper portion of the molded body does not work at all.
This results in the aforementioned fundamental problem associated with the luminescence performance that the available depth for light emission is so small and the luminescence period cannot be extended.
Because of these drawbacks, the photoluminescent function is practically utilized only by paints, resin tapes and resin films containing the photoluminescent pigments, although attention is focused on the photoluminescent function which is useful for the evacuation guide and the like in the event of power failure at underground shopping center. Furthermore, as a result of these drawbacks, such paints, resin tapes and resin sheets are short of adequately exhibiting the photoluminescent function.
The photoluminescent pigment is so expensive that the addition of a small amount of the pigment results in a 3-fold to 100-fold increase of the total cost. Therefore, it is not feasible to incorporate the photoluminescent pigment in a portion of the artificial stone where the photoluminescent pigment does not actually contribute to the light emission.
Consequently, the conventional photoluminescent material has quite limited performance and application.
In view of the foregoing, the present inventors have proposed a material containing an inorganic aggregate or filler and a resin, the material which accomplishes high strength, high hardness and a deep color tone like that of the natural stone, which permits an outside portion to work more efficiently by increasing the available depth for light emission by way of a minimum possible amount of photoluminescent pigment, and which achieves a further extension of the luminescence period (see, for example, WO98/39268, 98/35919).
The proposed materials are essentially characterized in that plural types of inorganic materials having significantly different mean particle sizes are used as the inorganic aggregate or filler in a specific mixing ratio, that the inorganic material having a greater particle size is a transparent substance, and that a photoluminescent pigment is admixed as the inorganic material having a smaller particle size, or otherwise is previously attached to the surface of the greater particles of transparent inorganic material by sinter-fuse coating or the like.
The proposed materials are realized based on a new finding that the available depth for light emission from the photoluminescent pigment or the like can be increased by controlling an internal structure of the molded body such as an artificial stone.
In fact, the artificial stone according to the proposal of the inventors is capable of maintaining the luminescence at a brightness of 3 mcd/m2 for more than 8 hours.
The inventors have made the follow-up study with an aim at a further improved photoluminescence performance such as a further extended period of luminescence at a given brightness, or more particularly a further improved photoluminescence performance by way of control of a relation between the internal structure of the molded body such as an artificial stone and the photoluminescence performance thereof.